mysql数据库(9):常用查询的例子

（7）使用用户变量

任务：要找出价格最高或最低的物品的

SELECT @min_price:=MIN(price),@max_price:=MAX(price) FROM shop;
SELECT * FROM shop WHERE price=@min_price OR price=@max_price;

（8）使用外键

CREATE TABLE person (
    id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
    name CHAR(60) NOT NULL,
    PRIMARY KEY (id)
);

CREATE TABLE shirt (
    id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
    style ENUM(‘t-shirt‘, ‘polo‘, ‘dress‘) NOT NULL,
    color ENUM(‘red‘, ‘blue‘, ‘orange‘, ‘white‘, ‘black‘) NOT NULL,
    owner SMALLINT UNSIGNED NOT NULL REFERENCES person(id),
    PRIMARY KEY (id)
);

INSERT INTO person VALUES (NULL, ‘Antonio Paz‘);

SELECT @last := LAST_INSERT_ID();

INSERT INTO shirt VALUES
(NULL, ‘polo‘, ‘blue‘, @last),
(NULL, ‘dress‘, ‘white‘, @last),
(NULL, ‘t-shirt‘, ‘blue‘, @last);

INSERT INTO person VALUES (NULL, ‘Lilliana Angelovska‘);

SELECT @last := LAST_INSERT_ID();

INSERT INTO shirt VALUES
(NULL, ‘dress‘, ‘orange‘, @last),
(NULL, ‘polo‘, ‘red‘, @last),
(NULL, ‘dress‘, ‘blue‘, @last),
(NULL, ‘t-shirt‘, ‘white‘, @last);

SELECT * FROM person;

SELECT * FROM shirt;

SELECT s.* FROM person p, shirt s
 WHERE p.name LIKE ‘Lilliana%‘
   AND s.owner = p.id
   AND s.color <> ‘white‘;

 （8）根据天计算访问量

CREATE TABLE t1 (year YEAR(4), month INT(2) UNSIGNED ZEROFILL,
             day INT(2) UNSIGNED ZEROFILL);
INSERT INTO t1 VALUES(2000,1,1),(2000,1,20),(2000,1,30),(2000,2,2),
            (2000,2,23),(2000,2,23);

SELECT year,month,BIT_COUNT(BIT_OR(1<<day)) AS days FROM t1
       GROUP BY year,month;

 （9）使用AUTO_INCREMENT

CREATE TABLE animals (
     id MEDIUMINT NOT NULL AUTO_INCREMENT,
     name CHAR(30) NOT NULL,
     PRIMARY KEY (id)
 );

INSERT INTO animals (name) VALUES 
    (‘dog‘),(‘cat‘),(‘penguin‘),
    (‘lax‘),(‘whale‘),(‘ostrich‘);

SELECT * FROM animals;

mysql数据库(9):常用查询的例子

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